Machines for polishing rice grains developed over the years include the friction type horizontal axis machines wherein the unpolished rice grains pass through a chamber from one end to another end. The chamber includes a cam roll surrounded on the periphery by a perforated screen, also referred to as a sieve. Normally, the sieve is configured to form a polygonal surface. Further, pluralities of tooth like projections on the outer surface of the cam. The cam with tooth like projections along with the sieve creates a gap in the rice polishing machine and restricts the passage of the grains during their movement along the axis of the rice polishing machine. Further, the gap of the passage varies between a maximum and a minimum thereby creating an annulus. The annulus so formed in the chamber provides a pressure gradient and this allows for effective polishing of rice grains.
FIG. 1 shows cross sectional view of a shaft assembly of an existing horizontal rice-polishing machine with a capacity of 4-5 tons per hour (tph), showing the relative arrangement between the cam, teeth and the sieve. The minimum gap between the cam and the sieve makes sure that rice grains are packed and pressure is sufficient to create friction between rice grains. The maximum gap between the cam and the sieve ensures that the rice grains are unpacked and allows for mixing and exchange of rice grains as it moves along the chamber. These actions take place repeatedly in the polishing chamber and helps in polishing of the rice grains.
However, when a polishing machine is designed for operating at higher loads, the maximum and the minimum gaps aforementioned, that exists between the cam and the sieve is severally altered, leading to improper polishing of the rice grains. This is predominantly due to the polygonal construction of the sieve which does not provide the required gap distance for ensuring effective polishing. Hence, there is a need for a construction of a sieve which allows for alignment of the gap to ensure effective polishing.